The relationship between radiographic crestal alveolar bone mass and changes in clinical periodontal attachment level following guided tissue regeneration (GTR) was evaluated in this retrospective study. A total of 12 intrabony two- or threewalled defects and 12 adjacent nondiseased proximal sites in 10 nonsmoking adult subjects received subgingival debridement and GTR using resorbable (Resolut; five sites) or nonresorbable (Gore-Tex; seven sites) barrier membranes. At a mean of 48.8 months posttreatment, clinical periodontal attachment level alterations were measured, and crestal alveolar bone mass changes on digital subtraction radiographic images derived from serial periapical radiographs were analyzed to correct for between-film geometric and contrast density differences. Intrabony defects exhibited a mean clinical periodontal attachment level gain of 2.3 ± 0.4 mm, in contrast to a mean loss of 0.5 ± 0.2 mm in adjacent nondiseased interproximal sites. Digital subtraction radiography revealed an increase in crestal alveolar bone mass at all intrabony sites treated with GTR and a decrease in three of the adjacent nondiseased sites. Site-based analysis yielded an odds ratio of 36 (P .001) for the association between radiographic increases in crestal alveolar bone mass and clinical periodontal attachment level gains of >= 2 mm. These results suggest a strong concordance between digital subtraction radiographic assessments of crestal alveolar bone mass and clinical periodontal attachment level in evaluating the long-term effects of GTR at human interproximal intrabony defects.